Advocates on both sides of a proposed U.S. immigration overhaul are closely eyeing the nation's most-watched cable news network -- and megaphone -- for politically-conservative causes as it joins a rapidly escalating national debate.

Will the network and its high-profile opinionators fan the flames of opposition to a comprehensive reform plan, or will it assume a more neutral role in a debate that does not break cleanly along party lines?

Rupert Murdoch, chairman and CEO at News Corp., Fox's parent company, is the wild card factor in which way Fox News will go.

Murdoch, Australian born and a naturalized U.S. citizen, has become an outspoken advocate for immigration reform and mass legalization of the country's undocumented immigrants, partnering with New York City Mayor Michael Bloomberg in this cause.

Whether Murdoch's personal views will percolate through his network, or at least temper criticism on the airwaves of those who don't share it, remains to be seen.

"It depends on how prepared he is to muzzle people on Fox," said Ira Mehlman, spokesman for the Federation for American Immigration Reform and frequent Fox News guest, who opposes the widespread legalization proposed by President Obama and a bipartisan group of U.S. senators this week.

"Rupert Murdoch, first and foremost, is a businessman," he said. "I'm not sure given all his other troubles he can afford to alienate his own audience."

Mehlman and other Republican critics of what they call an "amnesty" plan believe Fox News could be a crucial ally in the battle for public opinion on immigration.

They credit Fox News with helping to amplify their message and derail a similar legislative push that was backed mostly by Democrats and President George W. Bush in 2006 and 2007.

"That's what stopped the 2007 amnesty because all of a sudden all these members of Congress ... were getting called by their constituents saying what are you doing?" said Rosemary Jenks, the chief lobbyist with Numbers USA, which favors more stringent immigration controls.

But 2013 is shaping up to be a different game, immigrant advocates say, with Fox News possibly emerging as a potential boon.

"[Fox host] Sean Hannity is in favor, did an 180 degree turn. You're looking at [Fox host] Bill O'Reilly, who endorsed [Sen.] Marco Rubio's principles overwhelmingly. Even [Fox commentator] Charles Krauthammer has posted and said something needs to be done," said Brad Bailey, a self-described conservative Republican and businessman who chairs the Texas Immigration Solution.

"We need to see more Marco Rubios out there, we need people to come out and rally around them because the solution to this problem is what we need verses the rhetoric," Bailey said, suggesting the network could be a valuable forum to court moderates.

Bloomberg says much depends on the message Murdoch sends to Fox executives about how to handle the immigration story.

"The real thing is if he could get Fox to, you know, be the big champion, which sometimes they do," the mayor told Politico in an interview last week. But, he added, "sometimes they don't."

During a 2010 hearing on Capitol Hill, both men sat side-by-side as Murdoch told lawmakers it is "nonsense" not to provide a "full path to legalization" for the millions living and working in the shadows.

"Requiring unauthorized immigrants to register, undergo a security check, pay taxes, and learn English would bring these immigrants out of a shadow economy and into our tax base," he said at the time. He has since been pushing the message on Twitter.